When you use a modifier key - in this case shift / option, you must release the mouse or whatever you are using FIRST, then the modifier key or it won't work. When using a mouse it's almost instant and not noticiable. However, when using something like a trackpad - which is what I use, you have to pause for a little longer, like a 1/2 a second and then release the keyboard. This may not be your issue but I would encourage you to try it. Also - try resetting preferences.
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